This invention relates to an additional information superposition method for superposing spectrum spread additional information on a video signal such that, for example, when the video signal is converted into another video signal of a different aspect ratio, the superposed additional information can be extracted from the video signal after the conversion, and a video signal outputting apparatus which employs the additional information superposition method.
Various contents information such as image information and sound information can be provided abundantly through various media such as a video tape, a digital video disk (DVD), the Internet and broadcasting media. Meanwhile, infringement on copyright by illegal duplication (copy) of various contents information provided through various media has come into question.
In order to cope with this problem, various countermeasures have been proposed. For example, information for duplication control or copyright information is added to contents information such as image information, and the additional information is used to prevent illegal duplication of the contents information or to pursue an illegal duplicator of the contents information.
Further, a method has been proposed to superpose additional information to be added to contents information making use of an electronic watermark process. The electronic watermark process is a process of to embedding information as noise in a portion of image data or music data which is not significant on the perception of human beings, that is, a portion which is not redundant to music or an image.
Additional information embedded in image data or music data using such an electronic watermark process as described above is difficult to be removed from the image data or music data. On the other hand, even after a filtering process or a data compression process is performed for the image data or music data, the additional information of the electronic watermark (electronic watermark information) embedded in the image data or music data can be extracted from the image data or music data.
In this manner, by making use of an electronic watermark process, electronic watermark information can be superposed on contents information such that it cannot be removed or modified readily. Further, since the electronic watermark information superposed on the contents information can be extracted with certainty, for example, by a recording apparatus, illegal duplication of the contents information can be prevented using the electronic watermark information superposed on the contents information.
An electronic watermark process which makes use of a spectrum spreading technique is known as one of such electronic watermark processes as described above. The electronic watermark process spectrum spreads additional information to convert it into a broad-band signal of a low level which can be regarded as noise with respect to an information signal such as image data and superposes the signal on the information signal such as image data.
Spectrum spreading of additional information is performed by multiplying the additional information by spread codes generated in a sufficiently short period. The additional information in the form of a broad-band signal of a low level obtained by spectrum spreading can be extracted as an original narrow-band signal of a high level by performing despreading of multiplying the additional information by the spread codes same as those used upon spectrum spreading at same timings.
Thus, it has been proposed to generate, when it is tried to superpose spectrum spread additional information (electronic watermark information) on a video signal, spread codes in synchronism with a vertical synchronizing signal such as, for example, in a one-frame period or a two-frame period and superpose additional information spectrum spread with the spread codes on the video signal.
Therefore, in order to extract the electronic watermark information superposed on the video signal, spread codes same as those used upon spectrum spreading can be generated at same timings to despread the additional information spectrum spread and superposed on the video signal by using a video synchronizing signal as a reference signal. Consequently, the additional information spectrum spread and superposed on the video signal can be extracted rapidly with certainty.
However, some of video signals provided through DVDs or broadcasting media are for forming an image having an aspect ratio of 16:9. In order to display an image of the aspect ratio of 16:9 on a monitor receiver or a like having a frame of another aspect ratio of 4:3 which is spread widely, the video signal must be converted into another video signal for forming an image of the aspect ratio of 4:3.
In this instance, if the video signal for forming an image of the aspect ratio of 16:9 has additional information added thereto which is spectrum spread with spread codes generated, for example, in synchronism with a video signal synchronizing signal, then when the video signal is converted into another video signal for forming an image of the aspect ratio of 4:3, the additional information superposed on the video signal before such conversion cannot sometimes be detected from within the video signal after the conversion.
Several methods are available to convert a video signal for forming an image of the aspect ratio of 16:9 to another video signal for forming an image of the aspect ratio of 4:3 including, for example, a normal process, a letter box process and a pan scan process.
The normal process forms, from a video signal for forming an image of the aspect ratio of 16:9, another video signal for forming an entire image PW to be displayed on a screen GW of the aspect ratio of 16:9 as seen in FIG. 17A as another image PS on another screen GS of the aspect ratio of 4:3 as seen in FIG. 17B.
The video signal formed by the normal process allows an entire image PW of the aspect ratio of 16:9 to be displayed as another image PS of the aspect ratio of 4:3 without any miss as seen from FIGS. 17A and 17B.
In this case, even if additional information spectrum spread with spread codes PN1, PN2, . . . generated, for example, in a one frame period is superposed in synchronism with a vertical synchronizing signal VD on the video signal for forming an image PW of the aspect ratio of 16:9 as seen in FIG. 17C, when the video signal is converted into another video signal for forming another image PS of the aspect ratio of 4:3, the additional information spectrum spread with the spread codes PN1, PN2, . . . is not lost as seen in FIG. 17D.
Accordingly, from a video signal formed by the normal process for forming an image PS of the aspect ratio of 4:3, additional information spectrum spread and superposed on the video signal can be extracted by generating spread codes PN1, PN2, . . . in a one frame period in synchronism with a vertical synchronizing signal VD of the video signal and despreading the video signal with the spread codes.
Meanwhile, the letter box process forms, from a video signal for forming an image PW to be displayed on a screen GW of the aspect ratio of 16:9, another video signal for displaying the entire image PW as seen in FIG. 18A as another image PSW on another screen GS of the aspect ratio of 4:3 as seen in FIG. 18B.
In this instance, an image PSW of the aspect ratio of 16:9 is displayed in a predetermined area including a predetermined plurality of horizontal lines in a vertical direction in the screen GS of the aspect ratio of 4:3 as seen in FIG. 18B, and a pair of image non-displaying areas in which no image is displayed are provided at upper and lower portions of the screen GS.
Accordingly, where additional information spectrum spread with spread codes PN1, PN2, . . . generated, for example, in a one frame period is superposed on a video signal for forming an image PW of the aspect ratio of 16:9 as seen in FIG. 18C, if the video signal is converted into another video signal for forming another image PS of the aspect ratio of 4:3 by the letter box process, then the display position of an image PSW on which the spectrum spread additional information is superposed is delayed with respect to the vertical synchronizing signal VD as seen in FIG. 18D.
On the other hand, in order to allow the image PW of the aspect ratio of 16:9 to be displayed in the screen GS of the aspect ratio of 4:3, horizontal lines are thinned out in a vertical direction from the image PW of the aspect ratio of 16:9 to form the image PSW of the aspect ratio of 16:9 to be displayed in the screen GS of the aspect ratio of 4:3. Consequently, the number of horizontal lines in a vertical direction is different between the image PW of the aspect ratio of 16:9 and the image PSW of the aspect ratio of 16:9.
Therefore, even if spread codes PN1, PN2, . . . are generated in a one frame period in synchronism with a vertical synchronizing signal VD of a video signal for forming an image PS of the aspect ratio of 4:3, the spread codes cannot be generated at same timings as those when the additional information was spectrum spread, and the additional information spectrum despread and superposed on the video signal cannot be extracted.
The pan scan process cuts out, from an image PW to be displayed on a screen GW of the aspect ratio of 16:9 from a video signal for forming an image of the aspect ratio of 16:9, an image PB of a predetermined area which can be displayed without any distortion on another screen of the aspect ratio of 4:3 as seen in FIG. 19A. Then, a video signal for forming the thus cut out image PB as an image PBS on a screen GS of the aspect ratio of 4:3 as seen in FIG. 19B is formed from the video signal for forming the image PW of the aspect ratio of 16:9.
In this instance, the image PB (FIG. 20B) cut out from the image PW of the aspect ratio of 16:9 (FIG. 20A) and including M pixels in each horizontal line is formed from portions cut out from horizontal sections of the video signal for forming the image PW as can be apparently seen with reference to a horizontal synchronizing signal HD. Accordingly, the horizontal sections of the video signal which form the cut out image PB are shorter in time.
Therefore, interpolation of pixels is performed for the horizontal sections of the cut out image PB to form a video signal for displaying an image PBS, which includes m pixels in each horizontal line, corresponding to the cut out image PB fully on a screen GS of the aspect ratio of 4:3 as seen in FIG. 20C.
Accordingly, in the pan scan process, where additional information spectrum spread with spread codes PN1, PN2, . . . generated, for example, in a one frame period in synchronism with a vertical synchronizing signal VD is superposed on a video signal for forming an image PW of the aspect ratio of 16:9 as seen in FIG. 19C, when the video signal is converted into another video signal for forming another image PBS of the aspect ratio of. 4:3, the spread codes with which the additional information superposed on the video signal is spectrum spread are generated but in a displaced phase with respect to the vertical synchronizing signal VD as seen in FIG. 19D.
In short, the video signal for forming the image PBS of the aspect ratio of 4:3 has the additional information superposed thereon which is superposed on the video signal at a portion which forms the cut out image PB as seen in FIG. 19D. Since the additional information is spectrum spread with spread codes PNi to PNx, the generation phase of the spread codes with which the additional information is spectrum spread is displaced from the vertical synchronizing signal VD.
Further, the video signal for forming the image PBS is interpolated with pixels in the individual horizontal sections as described above with reference to FIGS. 20A to 20C. Therefore, not only the spread codes are generated in a displaced phase, but also the generation period of the spread codes per one chip is displaced.
Therefore, even if despreading is performed using spread codes PN1, PN2, . . . PNn generated in a one frame period in a similar manner as in a case wherein spectrum spread additional information is superposed on a video signal for forming an image PW of the aspect ratio of 16:9, the additional information spectrum spread and superposed on the vide signal for forming the image PBS cannot be detected.
Then, of images formed by the normal process, letter box process and pan scan process, the image displayed based on the video signal formed by the normal process is distorted in a vertical direction of the screen. Therefore, it is considered that the letter box process or the pan scan process which allows an image to be displayed without any distortion is in most cases used to convert a video signal for forming an image of the aspect ratio of 16:9 into another video signal for forming another image of the aspect ratio of 4:3.
The normal process, letter box process or pan scan process described above is normally performed on the transmission side. In particular, where a vide signal for forming an image of the aspect ratio of 16:9 is provided through a DVD, conversion processing to another video signal for forming another image of the aspect ratio of 4:3 is performed by a reproduction apparatus for a DVD.
Consequently, if a recording apparatus for receiving a video signal from the reproduction apparatus for a DVD receives a video signal formed by the letter box process or the pan scan process, then it cannot generate spread codes same as those used upon spectrum spreading at same timings from additional information spectrum spread and superposed on the received video signal. Thus, the recording apparatus cannot perform despreading appropriately to extract electronic watermark information superposed on the received video signal.
In this instance, even if electronic watermark information which signifies inhibition of duplication is superposed on the original video signal, since the electronic watermark information cannot be extracted, duplication (recording) of the video signal onto a in recording medium is permitted, and this gives rise to a problem that prevention of illegal duplication cannot be achieved.
It is an object of the present invention to provide an additional information superposition method by which additional information can be spectrum spread and superposed on a video signal such that, even if the video signal is converted into a second video signal for forming an image having a different aspect ratio, the additional information spectrum spread and superposed on the original video signal can be extracted from the second video signal and a video signal outputting apparatus which employs the additional information superposition method.
In order to attain the object described above, according to an aspect of the present invention, there is provided an additional information superposition method for superposing additional information spectrum spread with spread codes synchronized with a vertical synchronizing signal on a second video signal for forming an image of an aspect ratio of N:n which is to be converted into and outputted as a first video signal for forming an image of another aspect ratio of M:m, comprising the steps of setting a size of a unit block before conversion in the second video signal based on a size of a unit block after conversion to which one chip of spread codes for despreading determined in advance is allocated and contents of a conversion process into the first video signal, and superposing the additional information spectrum spread with the spread codes with the spread codes of one chip allocated for each unit block before conversion having the set size in such a manner as to allow the additional information to be extracted from the first video signal.
In the additional information superposition method, when, from the first video signal formed by conversion of the second video signal, the additional information spectrum spread and superposed on the first video signal is extracted, the size of the unit block after conversion to which one chip of the spread codes for despreading is allocated is determined in advance.
The size of the unit block before conversion in the second video signal is set based on the size of the unit block after conversion and contents of a conversion process into the first video signal so that the size of the unit block after conversion may be a predetermined size. The additional information spectrum spread with the a spread codes with the spread codes of one chip allocated for each unit block before conversion having the set size if is superposed on the second video signal.
Consequently, even when the second video signal for forming an image of the aspect ratio of N:n is converted into the first video signal for forming an image of the aspect ratio of M:m, the additional information superposed on the first video signal can be extracted with certainty without changing the extraction method such as changing the size of the unit block after conversion to which one chip of spread codes for despreading determined in advance is allocated.
The additional information superposition method may be constructed such that the first video signal is formed from the second video signal for forming an image of the aspect ratio of N:n by thinning out or interpolating pixels of the image of the second video signal in a horizontal direction or a vertical direction, and the size of the unit block before conversion is set in response to the number of pixels to be thinned out from or interpolated to the unit block before conversion in the horizontal direction or the vertical direction. In the additional information superposition method, even when the first video signal for forming an image of the aspect ratio of M:m is formed from the second video signal for forming an image of the aspect ratio of N:n by thinning out or interpolating pixels of the image of the second video signal in a horizontal direction or a vertical direction, the additional information superposed on the first video signal can be extracted with certainty without changing the extraction method.
The additional information superposition method may be constructed further such that the first video signal is for displaying the entire image of the aspect ratio of N:n to be formed with the second video signal without changing the aspect ratio in a predetermined region including a plurality of horizontal lines in a predetermined range of the screen of the aspect ratio of M:m in the vertical direction, and the size of the unit block before conversion is set in response to the number of horizontal lines to be thinned out in the vertical direction from the unit block before conversion. In the additional information superposition method, from the first video signal formed by a letter box process or a pan scan process, the additional information superposed on the first video signal can be extracted with certainty.
According to another aspect of the present invention, there is provided a video signal outputting apparatus for superposing additional information spectrum spread with spread codes synchronized with a vertical synchronizing signal on a second video signal for forming an image of an aspect ratio of N:n which is to be converted into and outputted as a first video signal for forming an image of another aspect ratio of M:m, comprising a synchronizing signal detection section for detecting a video synchronizing signal from the second video signal, a spread code generation control section for forming a generation timing signal synchronized with the video synchronizing signal from the synchronizing signal detection section for controlling a generation timing of the spread codes based on a size of a unit block before conversion in the second video signal which is set based on a size of a unit block after conversion to which one chip of spread codes for despreading determined in advance and contents of conversion processing into the first video signal in such a manner as to allow the additional information to be extracted from the first video signal, a spread code generation section for generating the spread codes in response to the generation timing signal from the spread code generation control section, a spreading section for receiving the additional information before spectrum spreading to be superposed on the second video signal and the spread codes from the spread code generation section and spectrum spreading the additional information with the spectrum codes, and an additional information superposition section for superposing the additional information spectrum spread by the spreading section on the second video signal.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.